Stabilization

ABSTRACT

Pigment compositions comprising 
     a) at least one organic pigment chosen from the group comprising azo pigments, quinacridones, phthalocyanines, indanthrones, flavanthrones, pyranthrones, anthraquinones, perylenes, dioxazines, perinones, thioindigo, isoindolines, isoindolinones and metal complexes and 
     b) 1 to 100% by weight, based on the pigment, of a nitroxyl compound consisting of at least one unsubstituted or substituted 5-, 6- or 7-membered heterocyclic ring containing a divalent group of the formula ##STR1##  in which R 1  and R 2  independently of one another are methyl, ethyl or phenyl, or together form a 4- to 12-membered aliphatic ring, 
     L is an aromatic radical 
     and Y is O., 
     or of an acid addition salt thereof. 
     These pigment compositions are distinguished by an outstanding resistance to light and weathering.

The present invention relates to the stabilisation of organic pigmentsagainst the influence of light and weather by the addition of nitroxylcompounds.

It is known that not all organic pigments always have a very goodfasmess to light and weathering. Nevertheless, some of them have provedto be valuable pigments. Although they already have a very goodresistance to light and weathering, it has now been found that,surprisingly, this can be improved further, especially in transparentpigment forms, if the pigments are mixed with a nitroxyl compound.

Nitroxyl compounds are known as stabilisers from various publications.In JP-A 75-58141, amongst many other HALS (hindered amine lightstabilisers), nitroxyl compounds which, together with UV absorbers,serve to stabilise pigmented plastics against the influence of light arealso described. It is stated that the action of UV absorbers as lightstabilisers for the plastic is impaired by the pigments, but that thisimpairment can be reduced by a HALS. HALS which contain no nitroxylgroup axe preferred. The use of N-hydroxy-HALS for preventingdeficiencies such as embrittlement, cracking, corrosion, erosion, lossof gloss, chalking and yellowing is known from EP-A 309 401. A polymermass which comprises a quinophthalone pigment and, thanks to theaddition of HALS, has a high light stability and resistance to fading isdescribed in U.S. Pat. No. 3 970 632. Although nitroxyl compounds arealso included quite generically, only HALS which are free from nitroxylgroups are mentioned specifically. Pigmented polymers comprising a UVabsorber and a HALS (without reference to nitroxyl compounds) for theprevention of fading are known from JP-A 82-119 941. Laminates which arestabilised against fading by the action of light and comprise, in anintermediate layer, a dyestuff (erroneously called pigment) which issoluble in an organic solvent and has been treated with a nitroxylcompound in the dissolved form are described in JP-A 90-99 323. For theexpert, these publications reveal the teaching that in the case ofplastics dyed with soluble dyestuffs, fading by the action of light canbe reduced under certain conditions, for example in intermediate layersof laminates, with treatment of the dissolved dyestuffs with a nitroxylcompound, but that the same effect is achieved in plastics pigmentedwith pigments, together with the stabilisation of the plastic, byadmixing a HALS which is free from nitroxyl groups.

It has now been found, quite surprisingly, that even the already highresistance of certain pigments to light and weathering can be improvedfurther by mixing or coating of the pigment particles with a nitroxylcompound.

The present invention accordingly relates to light-stabilised pigmentcompositions comprising

a) at least one organic pigment chosen from the group comprising azopigments, quinacridones, phthalocyanines, indanthrones, flavanthrones,pyranthrones, anthraquinones, perylenes, dioxazines, perinones,thioindigo, isoindolines, isoindolinones and metal complexes and

b) 1 to 100% by weight, based on the pigment, of a nitroxyl compoundconsisting of at least one unsubstituted or substituted 5-, 6- or7-membered heterocyclic ring containing a divalent group of the formula##STR2## in which

R₁ and R₂ independently of one another axe methyl, ethyl or phenyl, ortogether form a 4- to 12-membered aliphatic ring,

L is an aromatic radical

and Y is O.,

or of an acid addition salt thereof.

Particularly suitable pigments are those of the isoindoline,isoindolinone, metal complex, monoazo and, in particular, the bisazo,quinacridone, phthalocyanine, anthraquinone and perylene series. Theseare generally known and in some cases commercially obtainable products.The pigments axe preferably used in fine form, i.e. in transparent form,with an average particle size of 0.005 to 0. 1 μm, preferably 0.01 to0.07 μm.

The nitroxyl compounds are likewise known compounds. They arc disclosed,for example, in the following publications:

Chemical Reviews, 1978, Volume 78, No. 1, 37-64. (J. F. W. Keana, NewerAspects of the Synthesis and Chemistry of Nitroxide Spin Labels), inparticular pages 40-47;

Imidazoline Nitroxides, 1988, Volume 1, 5-23 (L. B. Volodarsky, I. A.Grigorev, Synthesis of Heterocyclic Nitroxides);

Tetrahedron Letters, Volume 29, No.: 37, 4677-4680, 1988 (R. W. Murray,M. Singh, A Convenient High Yield Synthesis of Nitroxides);

J. Org. Chem, 1991, Volume 56, 6110-6114 (Z. Ma, J. M. Bobbitt, OrganicOxoammonium Salts), in particular the examples on page 6114;

Journal of Polymer Science (Polymer Chemistry Edition), 1974, Volume 12,1407-1420 (T. Kurosald et al., Polymers Having Stable Radicals), inparticular the examples on pages 1417-1419;

U.S. Pat. No. 3 536 722, formula I and, in particular, Examples 1-6;

U.S. Pat. No. 3 936 456, columns I and 2 and, in particular, Examples 7and 8;

U.S. Pat. No. 3 971 757, formula I and Example 12;

U.S. Pat. No. 3 966 711, formula I and Example 7;

U.S. Pat. No. 4 131 599, columns 1 and 2 and Example 5; and

U.S. Pat. No. 5 001 233, in particular Example 1.

Any novel nitroxyl compounds as defined above which can be used can beprepared by methods analogous to generally known methods.

The nitroxyl compound is preferably employed in an amount of 5-100% byweight, based on the pigment.

R₁ and R₂ are preferably methyl.

Inorganic or organic salts of nitroxyl compounds, which are formed byaddition of acids in maximum mounts equivalent to the nitroxyl groups,can also be used. Such acids can be inorganic acids, such as, forexample, sulfuric, hydrochloric or phosphoric acid, or organiccarboxylic acids, such as formic, acetic, oxalic, maleic, benzoic orsalicylic acid, organic sulfonic acids, such as methane- orp-toluenesulfonic acid, or organic phosphorus-containing acids, such asbenzenephosphonic acid, methanephosphonic acid or benzenephosphinicacid.

Pigment compositions which are of particular interest are those in whicha nitroxyl compound of the formula ##STR3## is used, in which

R₃ is C₁ -C₁₈ alkyl or C₁ -C₁₈ alkoxy,

G is a divalent group of the formula --CR₄ =CH-- or --CH₄ --CH₂ -- and

R₄ is C₁ -C₁₈ alkyl,

Q is a group of the formula ##STR4## in which the bond labelled * is thebond leading to T, T is a direct bond or a group of the formula ##STR5##in which R₅ is hydrogen, halogen or C₁ -C₄ alkyl, or --(CH₂)_(r) --,

in which r is 1 or 2,

m is the number 1, 2, 3, 4 or 6,

X, if m=1, is hydrogen, C₁ -C₁₈ alkyl, phenyl which is unsubstituted orsubstituted by C₁ -C₄ alkyl, C₁ -C₄ alkoxy, phenyl or halogen, or, underthe condition that T, if bonded to a nitrogen atom, is not a directbond, is a group of the formula --OCO--NR₆ R₇, --OSO₂ --NR₆ R₇,--OCO--R₇, --COOR₇, --CONR₆ R₇, --NR₆ --COR₇, --NR₆ --CONR₆ R₇, --OR₇,--NR₆ R₇ or ##STR6## in which R₆ is hydrogen or C₁ -C₁₈ alkyl, R₇ is C₁-C₁₈ alkyl, C₂ -C₁₂ alkenyl, C₅ -C₁₂ cycloalkyl, or phenyl or naphthylwhich is unsubstituted or substituted by C₁ 1∝C₄ alkyl, C₁ -C₄ alkoxy,halogen, phenyl or nitro, or a group --(CH₂)_(S) --CHR₈ R₉, s is zero,1, 2 or 3, R₈ is hydrogen, methyl or phenyl and R₉ is --OH, halogen or agroup --COOCH₃ or --COOC₂ H₅ and,

if m=2, is a group of the formula --(CH₂)_(p) or, under the conditionthat T, if bonded to a nitrogen atom, is not a direct bond, is a groupof the formula --O--(CH₂)_(p) --O--, --NR₆ --(CH₂)_(p) --NR₆ --, inwhich F is --(CH₂)_(p) --, ##STR7## and p is a number between 2 and 10,and, if m=3, is a group ##STR8## and, if m=4, is a group ##STR9## ifm=6, is a group ##STR10## n is the number 1 or 2, V, if n=1, is C₂ -C₈alkylene or hydroxyalkylene or C₄ -C₂₂ acyloxyalkylene, and, if n=2, isthe group (--CH₂)₂ C(CH₂ --)₂ or ##STR11## and Z is a group of theformula ##STR12## in which the bond labelled with * is the bond leadingto W, W, if n=1, is a group --OCOR₁₀, in which R₁₀ is C₁ -C₁₈ alkyl, orphenyl or naphthyl which is unsubstituted or substituted by C₁ -C₄alkyl, C₁ -C₄ alkoxy or halogen, and,

if n=2, is a group of the formula --OCO--(CH₂)_(p) --COO-- or ##STR13##and Y is O.

Any C₁ -C₄ alkyl substituents are, for example, methyl, ethyl, n-propyl,isopropyl, n-butyl, sec-butyl or tert-butyl, and any C₁ -C₁₈ alkylsubstituents are additionally, for example, n-amyl, tert-amyl, hexyl,heptyl, octyl, 2-ethylhexyl, decyl, dodecyl, tetradecyl, hexadecyl oroctadecyl;

C₁ -C₄ alkoxy is, for example, methoxy, ethoxy, n-propoxy, isopropoxy orbutoxy, and C₁ -C₁₈ alkoxy is additionally, for example, hexyloxy,decyloxy, dodecyloxy, hexadecyloxy or actadecyloxy;

halogen is, for example, iodine, fluorine or, in particular, bromine,and preferably chlorine;

any C₂ -C₁₂ alkenyl substituents are, for example, vinyl, allyl,methallyl, 2-butenyl,

2-hexenyl, 3-hexenyl, 2-octenyl or 2-dodecenyl.

R₇ as C₅ -C₁₂ cycloalkyl is, for example, cyclopentyl, cycloheptyl,cyclooctyl, cyclononyl, cyclododecyl and, preferably, cyclohexyl.

V as C₂ -C₈ alkylene or -hydroxyalkylene is, for example, ethylene,1-methyl-ethylene, propylene, 2-ethyl-propylene or2-ethyl-2-hydroxymethylpropylene, and V as C₄ -C₂₂ acyloxyalkylene is,for example, 2-ethyl-2-acetoxymethylpropylene.

Pigment compositions in which a nitroxyl compound of the formula IV, Vor VI, as defined above, is used are of very special interest.

Particularly suitable nitroxyl compounds are those of the formula##STR14## in which

T is a direct bond,

m is 1, 2, or 3,

X₁, if m=1, is C₁ -C₁₈ alkyl, --OCO--R₇, --NR₆ --COR₇ or ##STR15## inwhich R₆ is hydrogen or C₁ -C₁₈ alkyl and R₇ is C₁ -C₁₈ -alkyl, orphenyl or naphthyl which is unsubstituted or substituted by C₁ -C₄alkyl, C₁ -C₄ alkoxy, phenyl or halogen, and, if m=2, is a group--OCO--(CH₂)_(p) --OCO-- or --NR₆ CO--(CH₂)_(p) +CONR₁₅ --, in which pis a number between 2 and 8, ##STR16## and,

if m=3, is a group ##STR17## X₂ is C₁ -C₁₈ alkyl,

n is the number 2,

V is the group (--CH₂)₂ C(CH₂ --)₂ or ##STR18## and

Nitroxyl compounds of the formula VIII or IX, in which T is a directbond, m is 1, X₁ is benzoyloxy or naphthoxyloxy and X₂ is C₈ -C₁₈ alkyl,are preferred.

As already mentioned above, the pigments are stabilised against theaction of light and weather, which can lead either to fading or also todarkening of the colourations, by admixing with a nitroxyl compound. Theadmixing, according to the invention, of the nitroxyl compound with thepigment has proved to be effective, i.e. stabilising, in both cases. Theinvention furthermore accordingly relates to a process for light- andweather-stabilisation of pigments chosen from the group comprising azopigments, quinacridones, phthalocyanines, indanthrones, flavanthrones,pyranthrones, anthraquinones, perylenes, dioxazines, perinones,thioindigo, isoindolines, isoindolinones and metal complexes by mixingor coating the pigment particles with 1 to 100% by weight, based on thepigment, of a nitroxyl compound consisting of at least one unsubstitutedor substituted 5-, 6- or 7-membered heterocyclic ring containing adivalent group of the formula ##STR19## in which

R₁ and R₂ independently of one another are methyl, ethyl or phenyl, ortogether form a 4- to 12-membered aliphatic ring,

L is an aromatic radical

and Y is O.,

or of an acid addition salt thereof.

This can be effected by the following various methods:

The nitroxyl compound is dissolved in an organic solvent in the desiredmount. The pigment is suspended in this solution by customary methodsand, if appropriate, the resulting suspension is ground in aconventional mill. The pigment mixture is isolated by distilling off thesolvent and then drying;

The required amount of nitroxyl compound, dissolved in an organicsolvent, is added to a pigment suspension prepared by customary methodsand is then precipitated and also suspended by the addition of a solventin which it is not soluble, for example water. The suspension is thenfiltered and the pigment mixture is isolated by customary methods;

Preferably, however, the pigment and the nitroxyl compound areincorporated in the desired mount by customary methods, either inpremixed form or separately, into the substrate to be pigmented.

The pigment compositions according to the invention are excellentlysuitable as pigments for colouring high molecular weight organicmaterial, especially if high requirements of resistance to light andweathering are imposed.

High molecular weight organic materials which can be pigmented with thepigment compositions according to the invention are, for example,cellulose ethers and esters, such as ethylcellulose, nitrocellulose,cellulose acetate and cellulose butyrate, naturally occurring resins orsynthetic resins, such as polymerisation resins or condensation resins,such as aminoplasts, in particular urea- and melamine-formaldehyderesins, alkyd resins, phenolie resins, polycarbonates, polyolefins,polystyrene, polyvinyl chloride, polyamides, polyurethanes, polyesters,ABS, polyphenylene oxides, rubber, easein, silicone and silicone resins,individually or as mixtures.

The pigment compositions according to the invention are particularlysuitable for colouring polyvinyl chloride and polyolefins, such aspolyethylene and polypropylene, and for pigmenting varnishes, paints andprinting inks. Due to their high light fastness, however, they are alsoparticularly suitable for use in electrophotographic materials (forexample photocells), colour filters (for example liquid crystaldisplays), information storage materials (optical discs), non-linearoptical materials and in optical limiters.

However, the pigment compositions according to the invention arepreferably suitable for colouring aqueous and/or solvent-containingvarnishes, in particular automobile varnishes. They are especiallypreferably used for effect finishes in which transparent organicpigments are employed.

The high molecular weight organic compounds mentioned can be presentindividually or in mixtures as plastic compositions, melts or in theform of spinning solutions, varnishes, paints or printing inks.Depending on the intended use, it proves advantageous to employ thepigment compositions according to the invention as toners or in the formof preparations.

The pigment compositions according to the invention can be employed inan mount of 0.01 to 40% by weight, preferably 0.1 to 20% by weight,based on the high molecular weight organic material to be pigmented.

The high molecular weight organic substances are pigmented with thepigment compositions according to the invention, for example, byadmixing such a pigment composition, if appropriate in the form ofmasterbatches, or the individual components to these substrates usingroll mills or mixing or grinding apparatuses. The pigmented material isthen brought into the desired final form by processes which are knownper se, for example calendering, pressing, extrusion, brushing, castingor injection moulding. To produce non-rigid mouldings or to reduce theirbrittleness, it is often desirable to incorporate so-called plasticisersinto Me high molecular weight compounds before shaping. Plasticisers canbe, for example, esters of phosphoric acid, phthalic acid or sebacicacid. The plasticisers can be incorporated into the polymers before orafter incorporation of the pigment compositions according to theinvention. In order to achieve various colour shades, it is furthermorepossible also to add fillers or other colouring constituents, such aswhite, coloured or black pigments, in any amounts to the high molecularweight organic substances, in addition to the pigment compositionsaccording to the invention.

For pigmenting varnishes, paints and printing inks, the high molecularweight organic materials and the pigment compositions according to theinvention are finely dispersed or dissolved in a common organic solventor solvent mixture, if appropriate together with additives, such asfillers, other pigments, siccatives or plasticisers. A procedure can befollowed here in which the individual components are dispersed ordissolved by themselves, or also several of them together, and only thenare all the components brought together.

In colourations, for example of varnishes, polyvinyl chloride orpolyolefins, the pigment compositions according to the invention aredistinguished by good general pigment properties, such as gooddispersibility, high tinctorial strength and purity, and good resistanceto migration, heat and, in particular, light and weathering.

The following examples illustrate the invention.

EXAMPLE 1: 0.9 g of a scarlet red bisazo pigment (C. I. Pigment Red 166)of the formula ##STR20## and 0.1 g of a nitroxyl compound of the formula##STR21## are suspended in 25 ml of methylene chloride by ultrasonictreatment for 3 minutes. The solvent is then distilled off and theresidue is dried.

The resulting stabilised pigment is incorporated into an alkyd-melaminestoving enamel as follows.

0.4 g of pigment/nitroxyl mixture, 7.6 g of TiO₂, 9 ml of methylisobutyl ketone and 30 g of stoving lacquer comprising 66.5 parts ofalkyd resin ®ALKYDAL F27 (Bayer AG), 24.4 parts of melamine resin®MEPRENAL TTK (Hoechst AG), 2.1 parts of xylene, 4.0 parts of ethyleneglycol and 1.0 parts of silicone oil (1% in xylene) are mixed bycustomary methods. The resulting colour lake is spread onto aluminiumsheets and stoved at 130° C. for 30 minutes.

A control coloured coating is likewise produced in the same manner, withthe exception that the pigment is employed without addition of thenitroxyl compound.

The resistance of the resulting coloured coatings to weathering isdetermined in accordance with the WOM test according to DIN 53387 afterweathering for 500 hours. The colouration obtained with addition of thenitroxyl compound has a significantly better resistance to weatheringthan the control coloured coating.

EXAMPLE 2

Example 1 is repeated, with the only exception that instead of thepigment of the formula XI, the same amount by weight of the bisazopigment (C. I. Pigment Yellow 93) of the formula ##STR22## is employed.The coloured coating shows a significantly better resistance toweathering than the corresponding control coloured coating.

EXAMPLES 3-55

0.4 g of one of the pigments shown in column 1 in the following Table 1and 0.08 g of one of the nitroxyl compounds shown in column 2 of Table 1are incorporated separately, but otherwise in the same manner, into thesame alkyd-melamine stoving enamel (white reduction) as described inExample 1 (method B). The resistance of the resulting coloured coatingsand corresponding control coloured coatings without a nitroxyl compoundto weathering is determined as described in Example 1. In all theexamples shown, a better resistance to weathering can be detected thanin the case of the corresponding control coloured coatings.

                                      TABLE 1                                     __________________________________________________________________________    Example                                                                            I            II                                                          __________________________________________________________________________    3    C.I. Pigment Orange 34                                                                      ##STR23##                                                  4    C.I. Pigment Orange 34                                                                      ##STR24##                                                  5    C.I. Pigment Orange 34                                                                      ##STR25##                                                  6    C.I. Pigment Orange 34                                                                      ##STR26##                                                  7    C.I. Pigment Yellow 95                                                                      ##STR27##                                                  8    C.I. Pigment Yellow 95                                                                      ##STR28##                                                  9    C.I. Pigment Yellow 95                                                                      ##STR29##                                                  10   C.I. Pigment Yellow 95                                                                      ##STR30##                                                  11   C.I. Pigment Yellow 62                                                                      ##STR31##                                                  12   C.I. Pigment Yellow 62                                                                      ##STR32##                                                  13   C.I. Pigment Yellow 62                                                                      ##STR33##                                                  14   C.I. Pigment Yellow 62                                                                      ##STR34##                                                  15   C.I. Pigment Yellow 17                                                                      ##STR35##                                                  16   C.I. Pigment Yellow 17                                                                      ##STR36##                                                  17   C.I. Pigment Yellow 17                                                                      ##STR37##                                                  18   C.I. Pigment Yellow 17                                                                      ##STR38##                                                  19   C.I. Pigment Red 177                                                                        ##STR39##                                                  20   C.I. Pigment Red 177                                                                        ##STR40##                                                  21   C.I. Pigment Red 177                                                                        ##STR41##                                                  22   C.I. Pigment Red 177                                                                        ##STR42##                                                  23   C.I. Pigment Red 188                                                                        ##STR43##                                                  24   C.I. Pigment Yellow 188                                                                     ##STR44##                                                  25   C.I. Pigment Yellow 188                                                                     ##STR45##                                                  26   C.I. Pigment Yellow 188                                                                     ##STR46##                                                  27   C.I. Pigment Blue 15:4                                                                      ##STR47##                                                  28   C.I. Pigment Blue 15:4                                                                      ##STR48##                                                  29   C.I. Pigment Blue 15:4                                                                      ##STR49##                                                  30   C.I. Pigment Blue 15:4                                                                      ##STR50##                                                  31   C.I. Pigment Red 170                                                                        ##STR51##                                                  32   C.I. Pigment Yellow 95                                                                      ##STR52##                                                  33   C.I. Pigment Red 177                                                                        ##STR53##                                                  34   C.I. Pigment Red 244                                                                        ##STR54##                                                  35   C.I. Pigment Yellow 110                                                                     ##STR55##                                                  36   C.I. Pigment Red 244                                                                        ##STR56##                                                  37   C.I. Pigment Yellow 110                                                                     ##STR57##                                                  38   C.I. Pigment Red 244                                                                        ##STR58##                                                  39   C.I. Pigment Yellow 110                                                                     ##STR59##                                                  40   C.I. Pigment Red 244                                                                        ##STR60##                                                  41   C.I. Pigment Yellow 110                                                                     ##STR61##                                                  42   C.I. Pigment Red 170                                                                        ##STR62##                                                  43   C.I. Pigment Yellow 188                                                                     ##STR63##                                                  44   C.I. Pigment Yellow 188                                                                     ##STR64##                                                  45   C.I. Pigment Yellow 188                                                                     ##STR65##                                                  46   C.I. Pigment Yellow 188                                                                     ##STR66##                                                  47   C.I. Pigment Yellow 188                                                                     ##STR67##                                                  48   C.I. Pigment Yellow 188                                                                     ##STR68##                                                  49   C.I. Pigment Yellow 95                                                                      ##STR69##                                                  50   C.I. Pigment Yellow 95                                                                      ##STR70##                                                  51   C.I. Pigment Yellow 95                                                                      ##STR71##                                                  52   C.I. Pigment Yellow 95                                                                      ##STR72##                                                  53   C.I. Pigment Yellow 95                                                                      ##STR73##                                                  54   C.I. Pigment Yellow 17                                                                      ##STR74##                                                  55   C.I. Pigment Yellow 17                                                                      ##STR75##                                                  __________________________________________________________________________

EXAMPLES 56-58:

0.7 g of C. I. Pigment Yellow 95 and 0.35 g of one of the nitroxylcompounds shown in the following Table 2 are mixed in the dry state with700 g of polyethylene VESTOLEN A 6016® (Huls) and 1.4 ) g of calciumcarbonate MILICARB®. The mixture is then extruded in a single-screwextruder twice at 200° C. The granules thus obtained are processed tosheets on an injection moulding machine at 200° C. The resistance toweathering is determined by weathering the sheets as described for thecoloured coatings in Example 1. In all the examples, a better resistanceto weathering can be determined than in the case of control sheetsproduced correspondingly without nitroxyl compounds.

                  TABLE 2                                                         ______________________________________                                        Example Nitroxyl compound                                                     ______________________________________                                        56                                                                                     ##STR76##                                                            57                                                                                     ##STR77##                                                            58                                                                                     ##STR78##                                                            ______________________________________                                    

EXAMPLES 59-61:

0.5 g of C. I. Pigment Yellow 95, 0.1 g of one of the nitroxyl compoundsshown in the following Table 3 and 16.2 g of a nitrocellulose printingink comprising 11 g of nitrocellulose A 250, 9 g of DOWANOL PM® (DowChem.), 20 g of ethyl acetate and 60 g of ethanol are mixed by customarymethods. The resulting printing ink is spread onto paper. The resistanceto weathering is determined by exposure of the colourations to light inaccordance with the fadeometer test for 500 hours. In all the examples,a better resistance to weathering can be determined than in the case ofcontrol colourations produced correspondingly without nitroxylcompounds.

                  TABLE 3                                                         ______________________________________                                        Example Nitroxyl compound                                                     ______________________________________                                        59                                                                                     ##STR79##                                                            60                                                                                     ##STR80##                                                            61                                                                                     ##STR81##                                                            ______________________________________                                    

EXAMPLES 62-64:

Examples 59-61 are repeated with the only exception that instead of C.I. Pigment Yellow 95, the same amount by weight of C. I. Pigment Yellow188 is used. A better light fastness than in the case of correspondingcontrol colourations without a nitroxyl compound can also be determinedin these examples.

The classes to which the pigments used in Examples 3-64 belong are shownin the following Table 4.

                  TABLE 4                                                         ______________________________________                                        C.I. designation                                                                              Pigment class                                                 ______________________________________                                        C.I. Pigment Yellow 17                                                                        Bisazo pigment                                                C.I. Pigment Yellow 62                                                                        Laked monoazo pigment                                         C.I. Pigment Yellow 95                                                                        Bisazo pigment                                                C.I. Pigment Yellow 110                                                                       Isoindolinone pigment                                         C.I. Pigment Yellow 188                                                                       Bisazo pigment                                                C.I. Pigment Orange 34                                                                        Bisazo pigment                                                C.I. Pigment Red 170                                                                          Monoazo pigment                                               C.I. Pigment Red 177                                                                          Anthraquinone pigment                                         C.I. Pigment Red 244                                                                          Diaminoanthraquinonyl pigment                                 C.I. Pigment Blue 15:4                                                                        Copper phthalocyanine pigment                                 ______________________________________                                    

What is claimed is:
 1. A light-stabilised pigment composition consistingessentially ofa) at least one organic pigment chosen from the groupconsisting of azo pigments, quinacridones, phthalocyanines,indanthrones, flavanthrones, pyranthrones, anthraquinones, perylenes,dioxazines, perinones, thioindigo, isoindolines, isoindolinones andmetal complexes; and b) 1 to 100% by weight, based on the pigment, of anitroxyl compound of the formula ##STR82## wherein R₃ is C₁ -C₁₈ alkylor C₁ 1∝C₁₈ alkoxy; G is a divalent group of the formula --CR₄ =CH-- or--CHR₄ --CH₂ --; R₄ is C₁ -C₁₈ alkyl; Q is a group of the formula##STR83## in which the bond labelled * is the bond leading to T; T is adirect bond or a group of the formula ##STR84## in which R₅ is hydrogen,halogen or C₁ -C₄ alkyl, or --(CH₂)_(I) --, in which r is 1 or 2; m isthe number 1, 2, 3, 4 or 6; X, when m=1, is hydrogen, C₁ -C₁₈ alkyl,phenyl which is unsubstituted or substituted by C₁ -C₄ alkyl, C₁ -C₄alkoxy, phenyl or halogen, or, under the condition that T, if bonded toa nitrogen atom, is not a direct bond, is a group of the formula--OCO--NR₆ R₇, --OSO₂ --NR₆ R₇, --OCO--R₇, --COOR₇, --CONR₆ R₇, --NR₆--COR₇, --NR₆ --CONR₆ R₇, --OR₇, --NR₆ R₇ or ##STR85## in which R₆ ishydrogen or C₁ -C₁₈ alkyl, R₇ is C₁ -C₁₈ alkyl, C₂ -C₁₂ alkenyl, C₅ -C₁₂cycloalkyl, or phenyl or naphthyl which is unsubstituted or substitutedby C₁ -C₄ alkyl, C₁ -C₄ alkoxy, halogen, phenyl or nitro, or a group--(CH₂)_(S) --CHR₈ R₉, s is zero, 1, 2, or 3, R₈ is hydrogen, methyl orphenyl and R₉ is --OH, halogen or a group --COOCH₃ or --COOC₂ H₅ ; X,when m=2, is a group of the formula --(CH₂)_(p) or, under the conditionthat T, if bonded to a nitrogen atom, is not a direct bond, is a groupof the formula --O--(CH₂)_(p) --O--, --NR₆ --(CH₂)_(p) --NR₆ --,--OCO--M--COO--, --NR₆ --CO--M--CO--NR₆ --, --OCO--NH--M--NH--COO-- or--NR₆ --CONH--NHCO--NR₆ --, in which M is --(CH₂)_(p) --, ##STR86## andp is a number between 2 and 10; X, when m=3, is a group ##STR87## X,when m=4, is a group ##STR88## X, when m=6, is a group ##STR89## X₂ isC₁ -C₁₈ alkyl; n is the number 1 or 2; V, when n=1, is C₂ -C₈ alkyleneor hydroxyalkylene or C₄ -C₂₂ acyloxyalkylene; or V, when n=2, is thegroup (--CH₂)₂ C(CH₂ --)₂ or ##STR90## Z is a group of the formula##STR91## in which the bond labelled with * is the bond leading to W; W,when n=1, is a group --OCOR₁₀, in which R₁₀ is C₁ -C₁₈ alkyl, or phenylor naphthyl which is unsubstituted or substituted by C₁ -C₄ alkyl, C₁-C₄ alkoxy or halogen; or W, when n=2, is a group of the formula--OCO--(CH₂)_(p) --COO-- or ##STR92## and Y is O.
 2. A pigmentcomposition according to claim 1, wherein a pigment of the isoindoline,isoindolinone, metal complex, monoazo and, in particular, of the bisazo,quinacridone, phthalocyanine, anthraquinone and perylene series is used.3. A pigment composition according to claim 1, wherein the pigment isused in a fine form having an average particle size of 0.005 to 0.1 μm.4. A pigment composition according to claim 1, wherein the nitroxylcompound is employed in an amount of 5-100% by weight, based on thepigment.
 5. A pigment composition according to claim 1, wherein anorganic or inorganic salt of the nitroxyl compound is used.
 6. A pigmentcomposition according to claim 1, wherein a nitroxyl compound of theformula IV, IX or VI is used.
 7. A pigment composition according toclaim 1, wherein a nitroxyl compound of the formula ##STR93## is used,in which T is a direct bond,m is 1, 2 or 3, X₁, if m=1, is C₁ -C₁₈alkyl, --OCO--R₇, --NR₆ --COR₇ or ##STR94## in which R₆ is hydrogen orC₁ -C₁₈ alkyl and R₇ is C₁ -C₁₈ alkyl, or phenyl or naphthyl which isunsubstituted or substituted by C₁ -C₄ alkyl, C₁ -C₄ alkoxy, phenyl orhalogen, and, if m=2, is a group --OCO--(CH₂)_(p) --OCO-- or --NR₆CO--(CH₂)_(p) -CONR₁₅ --, in which p is a number between 2 and 8,##STR95## and, if m=3, is a group ##STR96## X₂ is C₁ -C₁₈ alkyl, n isthe number 2, V is the group (--CH₂)₂ C(CH₂ --)₂ or ##STR97## and Y isO.
 8. A pigment composition according to claim 7, wherein a nitroxylcompound of the formula VIII or IX, in which T is a direct bond, m is 1,X₁ is benzoyloxy or naphthoyloxy and X₂ is C₈ -C₁₈ alkyl, is used.
 9. Aprocess for light- and weather-stabilisation of pigments chosen from thegroup consisting of azo pigments, quinacridones, phthalocyanines,indanthrones, flavanthrones, pyranthrones, anthraquinones, perylenes,dioxazines, perinones, thioindigo, isoindolines, isoindolinones andmetal complexes, which process consists essentially of mixing or coatingthe pigment particles with 1 to 100% by weight, based on the pigment, ofa nitroxyl compound of the formula ##STR98## is used, in which R₃ is C₁-C₁₈ alkyl or C₁ -C₁₈ alkoxy;G is a divalent group of the formula --CR₄═CH-- or --CHR₄ -CH₂ -; R₄ is C₁ -C₁₈ alkyl; Q is a group of the formula##STR99## in which the bond labelled * is the bond leading to T; T is adirect bond or a group of the formula ##STR100## in which R₅ ishydrogen, halogen or C₁ -C₄ alkyl, or --(CH₂)_(r) --, in which r is 1 or2; m is the number 1, 2, 3, 4 or 6; X, when m=1, is hydrogen, C₁ -C₁₈alkyl, phenyl which is unsubstituted or substituted by C₁ -C₄ alkyl, C₁-C₄ alkoxy, phenyl or halogen, or, under the condition that T, if bondedto a nitrogen atom, is not a direct bond, is a group of the formula--OCO--NR₆ R₇, --OSO₂ --NR₆ R₇, --OCO--R₇ , --COOR₇, --CONR₆ R₇, --NR₆--COR₇, --NR₆ --CONR₆ R₇, --OR₇, --NR₆ R₇ or ##STR101## in which R₆ ishydrogen or C₁ -C₁₈ alkyl, R₇ is C₁ -C₁₈ alkyl, C₂ -C₁₂ alken yl, C₅-C₁₂ cycloalkyl, or phenyl or naphthyl which is unsubstituted orsubstituted by C₁ -C₄ alkyl, C₁ -C₄ alkoxy, halogen, phenyl or nitro, ora group --(CH₂)_(s) --CHR₈ R₉, s is zero, 1,2 or 3, R₈ is hydrogen,methyl or phenyl and R₉ is --OH, halogen or a group --COOCH₃ or --COOC₂H₅ ; X, when m=2, is a group of the formula --(CH₂)_(p) or, under thecondition that T, if bonded to a nitrogen atom, is not a direct bond, isa group of the formula --O--(CH₂)_(p) --O--, --NR₆ --(CH₂)_(p) --NR₆ --,--OCO--M--COO--, --NR₆ --CO--M--CO--NR₆ --, --OCO--NH--M--NH--COO-- or--NR₆, --CONH --M--NHCO--NR₆ --, in which M is --(CH₂)_(p) --,##STR102## and p is a number between 2 and 10; X, when m=3, is a group##STR103## X, when m=4, is a group ##STR104## X, when m=6, is a group##STR105## X₂ is C₁ -C₁₈ alkyl; n is the number 1 or 2; V, when n=1, isC₂ -C₈ alkylene or hydroxyalkylene or C₄ -C₂₂ -acyloxyalkylene; or V,when n=2, is the group (--CH₂)₂ C(CH₂ --)₂ or ##STR106## Z is a group ofthe formula ##STR107## in which the bond labelled with * is the bondleading to W; W, when n=1, is a group --OCOR₁₀, in which R₁₀ is C₁ -C₁₈alkyl, or phenyl or naphthyl which is unsubstituted or substituted by C₁-C₄ alkyl, C₁ -C₄ alkoxy or halogen; or W, when n=2, is a group of theformula --OCO--(CH₂)_(p) --COO-- or ##STR108## and Y is O.
 10. A highmolecular weight organic material containing a pigment compositionaccording to claim
 1. 11. A high molecular weight organic materialaccording to claim 10, which is a varnish.
 12. A high molecular weightorganic material according to claim 11, which is an automobile finish.